U.S. Pat. No. 5,175,664 to Diels et al. describes a method and arrangement for discharge of lightning using ultra-short laser pulses. This proposed method enables discharges of electricity transmitted via conductive ionized channels produced by one or more first laser pulses of wavelengths essentially within the ultraviolet (UV) range. The preferred wavelength of operation is about 248 nm and the pulse duration of the laser is of the order of 100 fs. In accordance with this invention, lightning is triggered by creating an ionized channel by one or more femtosecond UV pulses and simultaneously sending one or more laser pulses of longer wavelength and duration through the same path. In this way the conductivity of the laser induced channel can be maintained long enough for discharges and lightning to occur. However, this patent does not address applications associated with atmospheric spectral sensing of atmospheric gases, pollutants and biological agents using femtosecond terawatt laser generated filaments as light sources.
One other related reference is U.S. Pat. No. 5,726,855 to Mourou et al., entitled “Apparatus and Method for Enabling the Creation of Multiple Extended Conduction Paths in the Atmosphere” which claims an apparatus and method for the creation of multiple extended conduction paths in the atmosphere using high peak-power ultra-short laser pulses. Furthermore, the same group published addressing long range self-channeling of intense femtosecond pulses in air in 1994 by Mourou and co-workers. The focus of their patent is centered on an apparatus for controlling the discharge of lightning strikes and grounding means using a grounding tower. Also no claims are made regarding spectroscopic optical sensing and identification of bio-agents using multiple extended conduction paths in the atmosphere.
It will therefore be appreciated that there remains a need for an improved system and technique for determining whether certain molecules, such as bioaerosols and chemical agents, may be found within a sample.